To understand and improve the Weather app, Apple collects limited information about the first time you launch the app in a day. This information is not linked to your identity. If you allow Weather to access your location, your location will be sent to Apple to provide relevant weather forecasts.
That’s actually a pretty nifty idea. Too bad we live in a privacy nightmare and can’t trust others.
Perhaps this would be a good use for other connected devices like smart power meters.
It’s a private feature in the Weather app on iPhone.